Leading experts on China today expressed surprise at the speed with which the country's J20 stealth aircraft was developed, but said the country's military prowess was still relatively backward and way behind that of the US.

The J20 was not as stealthy as the US F22 stealth fighter, but was "good enough for what China wants to do with it", Gary Li, of the International Institute for Strategic Studies, said.

He noted that it was also bigger than the F22, suggesting that it was designed potentially to carry more bombs and fuel against a "larger variety of targets".

The J20 would provoke more concern in India, South Korea, and Taiwan in particular, analysts said. But Li said the US was not going to be alarmed or dragged into a new arms race "just because of two prototypes".

Kerry Brown, of the Chatham House thinktank, said the J20 demonstrated the ability of the Chinese to conceal military research, but added that they were "still way, way behind the Americans". China's military interests were limited to its region, he added.

"The PLA [People's Liberation Army] is surprisingly defensive, [it thinks about] being hit rather that to hit – it believes it is weak and vulnerable", Brown said.

"It is not going to be a global policeman, but [will] have enough strength to maintain pressure on Taiwan and defend its own maritime borders."

He said that while the Obama administration was pushing hard to develop a proper dialogue with Beijing, the relative influence of China's political leaders and the military was becoming increasingly unclear. The country's current leaders had no military background, he added.

China's defence minister, Gen Liang Guanglie, said after talks in Beijing earlier this week with Robert Gates, his US opposite number, that while China had made progress in developing its military technology, "we can by no means call ourselves an advanced military force".

He was referring to the J20 and to reports of China's development of a long-range anti-ship missile.

Guanglie added: "The gap between us and that of advanced countries is at least two to three decades.

"I also want to emphasise that the efforts that we placed in research and development of our weapons systems is by no means targeted at any third country and it will by no means threaten any other country in the world."